Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Stars in Motion: High precision follow-up study of star movement shows surprising unrest in massive star cluster

Using the NASA/ESA Hubble Space Telescope, astronomers from the Max Planck Institute for Astronomy in Heidelberg and the University of Cologne have completed a long-term study of one of the most massive young star clusters in the Milky Way, comparing two observations that were made ten years apart.

The comparison, which relies on extremely precise measurements, reveals the motions of several hundreds of stars, which prove to be at odds with current models of how such clusters evolve, stellar motion not having “settled down” as expected. The results have been published in the Letters section of the Astrophysical Journal.

Ordinary star clusters ("open stellar clusters" or "stellar associations") disperse over time, as the different stars go their own separate ways. Very massive and compact clusters are thought to be different. In the long term, this can lead to the development of massive aggregations of stars known as "globular clusters", whose tightly-packed stars remain gravitationally bound to each other for billions of years.

With a mass of more than 10,000 suns packed into a volume with a diameter of a mere 3 light-years, the massive young star cluster in the giant nebula NGC 3603 is one of the most compact stellar clusters in the Milky Way.[1] (For comparison: in our own immediate stellar neighborhood, the same volume contains no more than a single star, namely the Sun.) Could this be a globular cluster in the making?

To find out, a team of astronomers led by Wolfgang Brandner (Max Planck Institute for Astronomy, Heidelberg, MPIA) tracked the movement of the cluster's many stars. Such a study can reveal whether the stars were in the process of drifting apart, or about to settle down. It also serves to distinguish members of the star cluster from unrelated stars that, as viewed from Earth, just happen to fall along the same light of sight.

Measurements of this kind are notoriously difficult. Imagine a star moving sideways at a rate of a few kilometers per second – a typical speed within stellar clusters. Viewed from a distance of 20,000 light-years (the actual distance of NGC 3603 from Earth), such a star's position on the night sky would shift by no more than a few billionths of an angular degree per year, at the limit of the capability of today's most precise observations.

By using two observations, made ten years apart with the same camera aboard the Hubble Space Telescope, and by performing an intricate analysis to account for all possible disturbances, Brandner and his colleagues were able to reach the required accuracy.

All in all, the team observed more than 800 stars. About 50 of these were identified as foreground stars, which are unrelated to the cluster. From the remaining sample of more than 700, the astronomers were able to obtain sufficiently precise speed measurements for 234 cluster stars of different masses and surface temperatures.[2] Boyke Rochau (MPIA), the paper's lead author, who performed the data analysis as part of his PhD work, explains: "Once our analysis was completed, we reached a precision of 27 millionths of an arc second per year. Imagine you are in Bremen, observing an object that is located in Vienna. Now the object moves sideways by the breadth of a human hair. That's a change in apparent position of about 27 millionths of an arc second." [3]

The results for the motion of these cluster stars were surprising: According to widely accepted models, which reproduce what is actually observed in older globular clusters, the average stellar speed in a cluster like the one in NGC 3603 should depend on mass: Stars with lower mass should move faster, and those with higher mass should move more slowly.[4] The stars for which precision measurements were possible represent a range of masses between 2 and 9 times that of the Sun. Yet all of them move at about the same average speed of 4.5 km/s (corresponding to a change in apparent position of a mere 140 micro-arc seconds per year). Average speed does not appear to vary with mass at all.

Apparently – and surprisingly – this very massive star cluster has not yet settled down. Instead, the stars' velocities still reflect conditions from the time the cluster was formed, approximately one million years ago. Team member Andrea Stolte from the University of Cologne explains: "For the first time, we have been able to measure precise stellar motions in such a compact young star cluster. This is key information for astronomers trying to understand how such clusters are formed, and how they evolve."

Vexingly, the question of whether or not the massive young cluster in NGC 3603 will become a globular cluster remains open. Given the new results, it all depends on the speeds of the low-mass stars, which were too faint to allow for precise speed measurements with the Hubble Space Telescope. Wolfgang Brandner says: "To find out whether or not our star cluster will disperse, we will need to wait for the next generation of telescopes, such as the James Webb Space Telescope (JWST) or ESO's European Extremely Large Telescope (E-ELT)." [5]


Dr. Wolfgang Brandner
Max Planck Institute for Astronomy, Heidelberg
Phone.: (+49|0) 6221 – 528 289
Boyke Rochau
Max-Planck-Institut für Astronomie, Heidelberg
Tel.: (+49|0) 6221 – 528 400
Dr. Markus Pössel (Public relations)
Max Planck Institute for Astronomy, Heidelberg
Phone: (+49|0) 6221 – 528 261
Background information
The article describing these results is B. Rochau et al., "Internal dynamics and membership of NGC 3603 Young Cluster from microarcsecond astrometry", published as a Letter in the June 10, 2010 issue of the Astrophysical Journal.

The members of the team are Boyke Rochau, Wolfgang Brandner, Mario Gennaro, Dimitrios Gouliermis, Nicola Da Rio, Natalia Dzyurkevich and Thomas Henning from the Max Planck Institute for Astronomy (MPIA) in Heidelberg, and Andrea Stolte from the University of Cologne.


[1] The nebula is located in the central plane of our home galaxy's main disk, in a region called the Carina spiral arm, at a distance of more than 20,000 light-years from the Sun.

[2] For stars with either particularly high or particularly low masses, the position cannot be fixed with the required accuracy. For very bright and massive stars, parts of the detector are saturated, making it very hard to find the center of the little disk as which the star appears on the image. Stars with very low masses are comparatively faint; those stars are not sufficiently clearly distinguishable from the background ("low signal to noise ratio") for position measurements of the required precision.

[3] More precisely, all these stars should have, on average, the same kinetic energy. Kinetic energy is proportional to an object's mass and to the square of its velocity. By this count, star with one half the mass of the Sun should, on average, move four times faster than stars with one solar mass.

[4] That is, observer and object are about 800 km (or 500 miles) apart, a bit more than the distance between Boston, MA and Pittsburgh, PA.

[5] The James Webb Space Telescope (JWST) is a planned infrared space telescope with a 6.5 m mirror, developed by a NASA-led international collaboration, and due to be launched in 2014. The European Extremely Large Telescope (E-ELT) is a proposed next-generation groundbased telescope with a 42 m mirror. It is being developed by an international collaboration led by the European Southern Observatory (ESO), and is slated for completion in 2018. German institutes, including the Max Planck Institute for Astronomy, are involved in the development of components and instruments for both projects.

Dr. Markus Pössel | Max-Planck-Institut
Further information:

More articles from Physics and Astronomy:

nachricht Climate cycles may explain how running water carved Mars' surface features
02.12.2016 | Penn State

nachricht What do Netflix, Google and planetary systems have in common?
02.12.2016 | University of Toronto

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

Im Focus: Molecules change shape when wet

Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water

In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...

Im Focus: Fraunhofer ISE Develops Highly Compact, High Frequency DC/DC Converter for Aviation

The efficiency of power electronic systems is not solely dependent on electrical efficiency but also on weight, for example, in mobile systems. When the weight of relevant components and devices in airplanes, for instance, is reduced, fuel savings can be achieved and correspondingly greenhouse gas emissions decreased. New materials and components based on gallium nitride (GaN) can help to reduce weight and increase the efficiency. With these new materials, power electronic switches can be operated at higher switching frequency, resulting in higher power density and lower material costs.

Researchers at the Fraunhofer Institute for Solar Energy Systems ISE together with partners have investigated how these materials can be used to make power...

All Focus news of the innovation-report >>>



Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

Latest News

UTSA study describes new minimally invasive device to treat cancer and other illnesses

02.12.2016 | Medical Engineering

Plasma-zapping process could yield trans fat-free soybean oil product

02.12.2016 | Agricultural and Forestry Science

What do Netflix, Google and planetary systems have in common?

02.12.2016 | Physics and Astronomy

More VideoLinks >>>